Rare Earth/Critical Mineral Processing

Lining Solutions for Rare Earth/Critical Mineral Processing

The mining industry around the world has been paying more attention to how rare earth and critical minerals are processed today.

Most of that activity is currently centered in China, as it mines roughly 70% of the world’s rare earth elements and processes up to 90% of them. That gap between mining and refining capacity is where new investment is concentrated today. New processing plants are being built across the U.S. and allied countries to expand separation and refining capacity and many need corrosion-resistant equipment engineered for bake-leach and separation conditions from day one.

Knight Material Technologies engineers acid-resistant brick, membrane and fluoropolymer lining systems for that equipment, built on decades of experience protecting acid production, storage and mining process equipment.

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What Are Rare Earth Minerals?

Rare Earth or Critical Minerals, according to the U.S. Geological Survey (USGS), are non-fuel mineral materials or elements essential to the U.S. economy and national security. Their supply chains are vulnerable to disruption. Rare earth elements comprise a specific subset of metallic elements (including such elements as scandium, yttrium and lanthanides) grouped under this broader, critical umbrella.
These are classified as “critical” because they act as vital components for advanced technologies such as hard drives, semiconductors and smartphones; clean energy including wind turbines, electric vehicle motors and solar panels; and contribute to U. S. national defense used in military hardware and electronic systems.
These minerals are typically mined from ore, requiring processing and refining through multi-step processes that rely on extremely aggressive chemicals. Many critical minerals are not mined alone; instead, they are obtained as co-products or by-products from mines extracting other base or precious metals.

Rare Earth Ore

Rare earth ore comes from several different deposit types and how aggressively it needs to be processed depends on which one. Aggressive processing methods include acid baking, acid leaching and pressure oxidation. Other ores can be processed with more mild solutions such as ammonium sulfate. Knight’s acid-resistant lining systems are built for the aggressive end of this range.

Bastnäsite ore is leached with concentrated sulfuric acid or hydrochloric acid under less extreme conditions.
Ion-adsorption clay ore, the dominant global source of heavy rare earth elements, is leached with a comparatively mild ammonium sulfate solution at near-ambient temperatures. This is a fundamentally different, less corrosive process that generally does not require heavy-duty acid-brick or membrane lining.
Some true rare earth elements, such as yttrium and lanthanum, can also be recovered as byproducts of high-pressure leaching circuits built primarily for base metals like nickel and cobalt. Scandium is recovered through the same kind of circuit.

Product Fit by Process Stage

Process Stage	KMT Solution
Acid bake/roasting	DURO^® and KNIGHT-WARE^® acid brick, ACIDSIL™ mortar
Water leaching/pressure leaching	PYROFLEX^® acid-resistant membrane + brick lining system
Pressure oxidation	PYROFLEX^® membrane + brick lining system
Off-gas scrubbing	FLEXERAMIC^® structured packing, FLEXISADDLE^® ceramic random packing
Solvent extraction/separation	Electro Chemical Manufacturing fluoropolymer sheet linings
Waste neutralization	Superior Dual Laminate products/FRP tanks

Choosing the Right Construction Method

Knight Material Technologies and its affiliated companies, Electro Chemical Manufacturing (ECM) and Superior Dual Laminate (SDL), offer three different construction approaches for rare earth process facilities. The right one depends on the vessel, the process condition, and the acid involved.

Brick-lined construction (Knight): DURO^® and KNIGHT-WARE^® acid brick set over a PYROFLEX^® membrane. This is best suited to large, fixed vessels handling high-temperature, highly concentrated acid, and to slurries with abrasive ore particulate, such as monazite or xenotime bake-leach tanks.
Fluoropolymer-lined construction (ECM): linings in PTFE-M, PFA, PVDF, ECTFE, ETFE or FEP, bonded to a metal or FRP shell. Best suited to lower-abrasion, high-purity duties such as solvent extraction circuits, where a smooth, chemically inert surface limits fouling and product contamination.
FRP dual laminate construction (SDL): a chemically resistant thermoplastic liner (PVC, CPVC, PP or PVDF) over a fiberglass-reinforced structural shell. Lightweight and cost-effective for large, custom-fabricated tanks, scrubbers and ducting where weight and installation speed matter more than extreme abrasion resistance.

No single construction method fits every stage of a rare earth process system.

Knight Supports Rare Earth and Critical Mineral Recovery Projects Throughout the Process

Knight and its subsidiaries have provided lining solutions for process plants for a wide range of rare earth and critical minerals. These include tantalum, beryllium, indium, cobalt, nickel, zinc and copper. Knight provides its expertise to protect, as a single-source partner from design through installation.

Engineering and design of steel vessel shells and lining systems matched to the specific acid, temperature and pressure conditions of the recovery circuit
Flexible fabrication siting to fit a project’s local-content requirements or logistics constraints, drawing on a global network of qualified fabrication partners
Proprietary membrane and brick lining systems, the same PYROFLEX and KNIGHT-WARE family used in KMT’s autoclave lining work for gold, copper and nickel processing
Factory-installed lining by KMT’s own dedicated crews, not handed to a third-party installer, before equipment ships to site
Support for full letdown-train equipment, including flash vessels and blast spools, not just the primary leach vessel

Knight Material Technologies Is the Ideal Technology Partner for Rare Earth Processing

More than 100 years of acid-resistant lining engineering, transferable directly from Knight’s work with acid tower lining and mining autoclave relining projects to rare earth acid circuits
A single source across brick and membrane linings (Knight), fluoropolymer linings (ECM) and dual laminate equipment (SDL) on one project
Made in the USA manufacturing for the brick, membrane and packing components of the lining system
Engineering and installation crews with direct experience in the same pressure-vessel and autoclave equipment category rare earth recovery circuits use

Bringing Real-World Experience from the Field to Rare Earth Processing

Knight’s PYROFLEX^® membrane and acid-brick lining system has a documented track record in comparable acid-leach mining processes. At a gold and copper pressure-oxidation autoclave reline, the same lining system recovered an additional $8 million to $10 million annually in reduced downtime, with the reline paying for itself in roughly three years.

At Guizhou Zijin Mining’s pressure-oxidation autoclave, a Knight-designed PYROFLEX^® membrane and acid-brick lining system held integrity for seven years before major maintenance was required. Knight has also engineered lining systems for pressure-vessel equipment on critical-mineral recovery projects using high-pressure acid leaching.

Discuss Your Specific Process Facility

Do not risk unplanned downtime on a rare earth or critical mineral recovery process, where a lining failure means a full process shutdown, not just a repair.

Our team will:

Evaluate your process conditions (acid type, concentration, temperature and pressure) for each piece of equipment in the circuit
Recommend a system engineered specifically for your rare earth or critical mineral recovery process
Provide design, fabrication and factory or field installation from a single source
Support the equipment through startup and ongoing maintenance

Frequently Asked Questions

What is rare earth element processing?

Rare earth element processing extracts elements such as neodymium, dysprosium and yttrium from ore. Processing methods vary significantly by deposit type, from concentrated acid baking to much milder ammonium sulfate leaching.

What lining material survives rare earth acid-leach conditions?

Acid-resistant brick and membrane lining systems, such as Knight’s PYROFLEX^® membrane paired with KNIGHT-WARE^® acid brick, are engineered to withstand the sulfuric acid concentration and elevated temperature.

Is rare earth processing the same as critical mineral processing?

Most industry observers identify 17 rare earth elements, comprised of a family of 15 lanthanides plus scandium and yttrium.. When considering the difference between rare earth elements and critical minerals, they’re really different categories: rare earth elements are a chemistry definition, while critical minerals are a U. S. government policy designation, which is where the confusion and overlap comes from.

Critical minerals is a U.S. policy list that the Department of the Interior, through USGS, maintains. The current version is the final 2025 list, which grew from 50 to 60 minerals by adding boron, copper, lead, metallurgical coal, phosphate, potash, rhenium, silicon, silver and uranium.

How do they overlap?

Sixteen of the 60 critical minerals are rare earths. The only rare earth left out is promethium. The other 44 are not rare earths, including lithium, cobalt, nickel, graphite, copper and the platinum-group metals. So every rare earth except promethium is a critical mineral, but most critical minerals are not rare earths.

Does KMT install rare earth processing linings on-site or in a factory?

Knight can install lining systems either in a factory setting prior to shipment depending on size or arrange to have a team on-site, determined according to the project’s physical and logistics requirements.